284 H. W. NORRIS 
posterior to the first, and ventral to it, into that part of the brain 
lying between the two fiber tracts termed ‘a’ and ‘b’ by Kingsbury 
in Necturus. On entering the brain the rootlets turn posteriorly, 
to be traced a short distance only. 
In the second and ventral group of rootlets are the acoustic 
and the motor and communis facial fibers, together with a rootlet 
considered by the writer as general cutaneous. 
The origin of the motor component may be described in the 
words of Kingsbury (’95 a, p. 182) for Necturus: 
At about the exit of the tenth nerve, myelinic fibers begin to appear 
in the cinerea dorsad of a nidus of large cells in the ventro-lateral portion 
of the floor. From here to slightly cephalad of IX! [Xvrll., Siren], 
fibers spring continuously from this region and unite to form a close 
bundle which passes mesad to lie dorsad of the posterior longitudinal 
bundlew: 2. < In this position they run cephalad to just caudad of the 
exit of the eighth nerve where they turn laterad and ventrad in two 
(or three) bundles, to leave the oblongata as the motor roots of the 
seventh nerve. 
In Siren there are commonly three rootlets, one (VJIm.3) 
emerging through the roots of the eighth nerve, or through the 
communis component of the seventh nerve, a second (VIJm.2) 
through the spinal V tract, and a third larger one (V/Jm.1) ven- 
tral to the spinal V tract (figs. 28-31). At the point where these 
motor tracts turn laterally from the posterior longitudinal columns, 
Mauthner’s (mth.) fibers decussate and, running along the ventral 
border of the motor fibers, give an appearance of passing out into 
the seventh nerve (figs 30, 31). They are not to be traced farther 
than the immediate vicinity of certain giant cells (mthe.) lying 
on the ventral border of the gray matter in this region. 
The motor root of the facialis is the one described by Osborn 
(’88, p. 66) in Cryptobranchus and Siren as the third and fourth 
roots of the eighth nerve. According to him it arises in both 
cases from the ‘‘posterior longitudinal fasciculus,’’ which state- 
ment is, of course, an error. 
The communis component of the facialis (V//c.), entering and 
composing the fasciculus communis (fc.) at this level, is finer 
fibered than the other constituents of the VII-VIII complex, 
but densely medullated. 
